With this proposal we seek to further explore the relationship between mammographic parenchymal patterns and the risk of breast cancer. The main focus of the proposal is to expand the knowledge in the following, virtually unexplored areas: a) whether dietary factors, such as a diet rich in fat, influence mammographic patterns and how this affects a woman's risk of breast cancer; b) whether detectable differences exist in serum levels of reproductive hormones, such as estrogens or prolactin, between women with different mammographic patterns, and whether such differences influence the risk of breast cancer and c) whether age-related changes in parenchymal patterns influence a woman's risk of breast cancer. The study is prospective in design, in that parenchymal patterns, dietary data, and endocrine function are assessed prior to breast cancer detection, often years in advance. Information will be collected on approximately 250 histologically confirmed breast cancer cases, diagnosed between 1985 and 1992, and on 650 controls, selected at random from among the members of a cohort of women undergoing mammographic screening who are part of an ongoing NIH-sponsored research project. The study requires retrieving and reviewing mammograms for parenchymal patterns classification by two radiologists. Extensive background information, including known breast cancer risk factors and dietary data, and the results of laboratory analyses of estrogens, prolactin and sex-hormone-binding globulin, will be available through the ongoing study. A three-year project is planned.